1. Field of the Invention
The present invention relates to a field of forming semiconductor, and more particularly to a forming method of an epitaxial layer, a forming method of a 3D NAND memory and an annealing apparatus.
2. Description of the Prior Art
An NAND flash memory is a storage device better than a hard disk drive. With the pursuit of the non-volatile storage device with low-power, low-mass and high-performance, the NAND flash memory has been widely used in the electronic product. Currently, the planar NAND flash memory has had the practical expansion approaching an upper limit. In order to further increase the storage capacity and reduce the storage cost per bit, a 3D NAND memory with a 3D structure is proposed.
In the structure of the 3D NAND memory, a stacked structure of the 3D NAND memory is realized by using a method of vertically stacking a plurality of data storage units. The existed forming method of the 3D NAND memory generally includes: forming a stacked layer structure having silicon nitride layers and silicon oxide layers stacked alternately on the substrate; etching the stacked layer structure to form channel holes in the stacked layer structure, and etching the substrate situated at bottoms of the channel holes after forming the channel holes, so as to form trenches in the substrate; utilizing a selective epitaxial growth process to form an epitaxial silicon structure in the trenches at the bottom of the channel hole, and the epitaxial silicon structure is usually referred as SEG; forming a storage region in the channel hole; and removing the silicon nitride layers and forming a plurality of metal gates at positions corresponding to the removed silicon nitride layers.
When using the existed process to form the epitaxial silicon structure (SEG), a void defect is easily generated in the bottom region of the epitaxial silicon structure (SEG), such that the electrically contacting performance between the epitaxial silicon structure (SEG) and the substrate is worse, which affects the property of the 3D NAND memory.